Numerous different kinds of loader are known, in which the set of booms is arranged to be controlled, for example, using pressure-medium operated operating devices, such as hydraulic cylinders. Particularly harvester cranes can be stated to usually comprise a single lift cylinder and a single transfer cylinder. In accordance with its name, the movement of the lift cylinder essentially determines the height position of the outer end of the set of booms while correspondingly the transfer cylinder determines essentially the horizontal position of the outer end of the set of booms. Various harvester-crane implementations, particularly relating to forestry-machine applications, are disclosed in, for example, the following utility-model and patent publications: WO0156915, U20000471, FI961846, U.S. Pat. No. 5,197,615, FI20000978.
The aforementioned Mowi Ab loader (disclosed in Swedish patent publication SE7411568-4) has an advantageous path. If the path of the end of the articulated boom is thought of as being in front of the main boom, there is then a trapezium mechanism behind the main boom, which operates the articulated boom. The components of this mechanism are, in addition to the actual main boom, a lower arm pivoted at the same lower pivot as the main boom, a drag link parallel to the main boom, and arm means in the upper part of the main boom. In this case, the upper end of the drag link connected directly to the extension of the articulated boom. In more up-to-date loaders, a wide-angle joint is used, by means of which the relative rotation of the articulated boom can be increased. When the set of booms is being raised, the lift cylinder operates in compression, but is in danger of being hit by the load. In addition, the centre of gravity of the loader located disadvantageously high.
In one commercial harvester loader (Kesla Oyj, Forester H570), a rotating base in set on top of the pedestal, in which base there is a snout that carries the lower pivot and extends considerably, by means of which the reach is increased. The lift cylinder retracts inside a fork-shaped pedestal.
It is known that the operating device creating the lifting movement, the lift cylinder, can be arranged to the set of booms of the harvester crane to use either a pulling or pushing movement to lift the outer end of the set of booms. In the case of a pulling cylinder, the problem arises of the dimensions of the cylinder becoming unreasonably large in order to create a sufficient lifting force. In addition, the lift cylinder and the structures connected to it that come under a large tensile strain, particularly the structures made by casting, have proven to be unreliable in practice. On the other hand, in the case of a lift cylinder lifting with a pushing movement, the construction of the crane can become more complicated or heavier, while the cylinder is liable to receive a bucking load. In addition, in this case, the centre of gravity of the crane may become disadvantageously high (as in the Mowi). If the lift cylinder is located below the main boom, i.e. on the same side as that on which timber processing operations are carried out in timber harvesting, there is the danger that the lift cylinder will be damaged, for example, by being hit by a piece of timber or even by the felling head.
In forestry applications, cranes of this kind have been preferably hydraulically operated, so that the operating devices are mainly hydraulic cylinders. On the other hand, some solutions relating to this field of technology are known, in which the power transmission has been implemented in some other way, for instance with the aid of cables, or, for example, of electrical power.